Optical head with light sources of different wavelength

ABSTRACT

The present invention is provided with a detection region for detecting light that is reflected from a first or a second information recording medium and that passes through an optical element. The first information recording medium and the second information recording media are multi-layer disks that have at least two layers, and the detection region includes a detection region ( 41 ) for detecting first order and above diffracted light that has a first wavelength, and a detection region ( 42 ) for detecting first order and above diffracted light that has a second wavelength. The detection region ( 41 ) is arranged such that it does not straddle across a region that is divided by a maximum range ( 38 ) of the dilation of zero order light coming from the first information recording medium that comes from a recording layer that differs from the recording layer that is to be recorded or reproduced, and the detection region ( 42 ) is arranged such that it does not straddle across a region that is divided by a maximum range ( 39 ) of the dilation of zero order light coming from the second information recording medium that comes from a recording layer that differs from the recording layer that is to be recorded or reproduced.

TECHNICAL FIELD

The present invention relates to optical heads for recording,reproducing or deleting information stored on information recordingmedia such as, for example, optical disks and optical cards, andapparatuses and systems provided with such optical heads.

BACKGROUND ART

Applications of optical memory technology using optical disks as highdensity and high capacity information recording media are expanding todigital audio disks, video disks and document file disks and also todata files, and entering mainstream use. In order successfully toachieve highly reliable recording and reproduction of information ontooptical disks via a highly stopped down light beam, a focusing functionthat forms a minute spot at the diffraction limit, and optical systemfocusing control, tracking and pit signal (information signal) detectionfunctions are necessary.

In recent years, the development of optical disks with high densityrecording capacity that is greater than that of conventional opticaldisks has advanced due to the advancement of optical system designtechnology and a reduction in the wavelengths of semiconductor lasersserving as the light source. Increasing the size of the optical diskside numerical aperture (NA) of the focusing optical system that stopsdown the light beam to a minute point also has been investigated asanother approach to increase the density.

Compact disks (CDs), which may be considered first generation opticaldisks, use infrared light (with a wavelength λ3 of 780 nm-820 nm) and anobjective lens having an NA of 0.45, and the substrate thickness of thedisks is 1.2 mm. Second generation DVDs use red light (with a wavelengthλ2 of 630 nm-680 nm) and an objective lens having an NA of 0.6, and thesubstrate thickness of the disks is 0.6 mm. For third generation highdensity disks, a system using blue light (with a wavelength λ1 of 380nm-420 nm) and an objective lens having an NA of 0.85, and having disksubstrate thicknesses of 0.1 mm is proposed.

It should be noted that in the present application, substrate thicknessrefers to the thickness of the transparent substrate from the surface atwhich the light beam is incident on the optical disk (or informationrecording medium) to the information recording surface.

In this manner, the substrate thickness of the optical disk gets thinneras the recording density increases. Furthermore, dual layering of therecording layer is carried out as another method for realizing higherdensities. For DVDs, dual-layer disks are the standard for read only ROMdisks, and for high density third generation disks, dual-layer diskshave also been proposed for recordable disks.

An optical disk appatus that can record and reproduce optical diskshaving different substrate thicknesses and recording densities isdesirable from the point of view of economics, and the space that theapparatus occupies. Thus, it is necessary to have an optical head devicethat is provided with an optical detection system that can detect lightof different wavelengths that are irradiated onto optical disks.

Detection is possible if individual photodetectors are provided for eachdifferent wavelength of light. However the optical system thus becomescomplex, the flexible cable for outputting signals from the detectorsalso becomes complicated, and there is an increase in cost.

In the case of recording and reproducing different types of opticaldisks, a conventional example in which a single photodetector is sharedis proposed in, for example, Patent Reference 1 below. However, in thisexample it is a prerequisite that focus detection is by an astigmaticaberration method, and when using disks such as DVD-RAM in which thegroove pitch is relatively large compared to the light spot on the disk,there have been problems such as external interference affecting thefocus signal when transversing the tracks, causing the focus servos tobecome unstable.

Furthermore, the optical heads up to now have not taken intoconsideration multi-layer disks having a plurality of formats, andcountermeasures for offset fluctuations due to light scattering fromother layers have not been implemented.

The details proposed in Patent Document 1 hereby are described brieflywith reference to FIGS. 18 and 19. FIG. 18 shows a structural overviewof an optical head 1. FIG. 18A shows a state of the optical head 1 whenrecording and reproducing information on a DVD, and FIG. 18B shows howthe optical head 1 records and reproduces information onto a CD. Theoptical head 1 contains a red semiconductor laser 2 that generates lighthaving a wavelength of 650 nm, and an infrared semiconductor laser 3that generates light having a wavelength of 780 nm.

First, the case in which a DVD disk is reproduced is described. Lightgenerated by the red semiconductor laser 2 passes through a wavelengthselection prism 4 and is converted to parallel light by a collimatinglens 5. The light that is converted to parallel light is reflected by abeam splitter 6, passes through a wavelength filter 7 and a ¼ wavelengthplate 8, is converted to convergent light by an objective lens 9, and isirradiated onto a DVD disk 10. The light that is reflected/diffracted bythe DVD disk 10 again passes through the objective lens 9, the ¼wavelength plate 8 and the wavelength filter 7, passes through the beamsplitter 6, is diffracted by a hologram 11 so as to be converted toconvergent light and is focused on a photodetector 12.

Next, the case in which a CD disk is reproduced is described. Light thatis generated from the infrared semiconductor laser 3 is reflected by thewavelength selection beam splitter 4, and is converted to parallel lightby the collimating lens 5. The light that has been converted to parallellight is reflected by the beam splitter 6, passes through the wavelengthfilter 7 and the ¼ wavelength plate 8, is converted to converging lightby the objective lens 9 and is irradiated onto a CD disk 13. The lightthat is reflected by the CD disk 13 passes again through the objectivelens 9, the ¼ wavelength plate 8 and the wavelength filter 7, passesthrough the beam splitter 6, is diffracted by the hologram 11 to beconverted to convergent light, and is focused on the photodetector 12.

As shown in FIG. 19A, the hologram 11 is divided into a plurality ofregions, and one part of the regions (H1) guides only red light to thephotodetector 12 and the other part of the regions (H2) guides onlyinfrared light to the photodetector 12. In doing so, both regions causethe light to converge, as well as impart astigmatic aberration. As shownin FIG. 19B, the photodetector 12 has four detection regions. The lighthaving astigmatic aberration is irradiated onto the center of the fourdetection regions.

In this mode, a focus error signal for the astigmatic aberration methodis created by the difference between a sum of diagonally oppositeregions (A+C) and a sum of the other diagonally opposite regions (B+D),of the four detection regions. Furthermore, for a tracking signal, atracking error signal according to the push pull method is created fromthe difference between a sum of the regions on the same side (A+B) withrespect to the track projection and a sum of the regions on the otherside (C+D).

Furthermore, a tracking error signal for the phase differential methodis created by comparing the phases of the sum of the diagonally oppositeregions (A+C) with phases of the sum of the other diagonally oppositeregion (B+D). Moreover, an RF signal, which is a reproduction signal, iscreated from the sum of the entire region.

It is required that this optical head device reliably detect informationrecording media, whose applicable wavelengths differ and which includemulti-layer disks, using a minimum of photodetectors.

However, in this configuration, when reproducing multi-layer disks suchas dual-layer disks, scattered light from layers that are not the layerthat is to be read is incident on the photodetector, accordingly theseoffset the original signal, and thus there has been the problem that areliable signal could not be detected. In this case, it has beennecessary to increase the number of photodetectors in order to avoidscattered light.

Patent Reference 1

JP 2002-216385A (First diagram)

DISCLOSURE OF INVENTION

It is an object of the present invention to solve the above problem. Thepresent invention provides an optical head that reliably can record andreproduce information even when recording and reproducing multi-layerdisks of different varieties.

In order to achieve the above-noted object, the optical head of thepresent invention includes a first light source that emits light of afirst wavelength for at least either one of recording and reproducinginformation of a first information recording medium, a second lightsource that emits light of a second wavelength for at least either oneof recording and reproducing information of a second informationrecording medium, an optical element for diffracting light of the firstand the second wavelength, and a photodetector that is provided with adetection region for detecting light that is reflected by the firstinformation recording medium or the second information recording medium,and that passes through the optical element, wherein the firstinformation recording medium and the second information recording mediumare multi-layer disks having at least two layers, wherein the detectionregion includes a first diffracted light detection region for detectingfirst and higher order diffracted light of the first wavelength that isdiffracted by the optical element, and a second diffracted lightdetection region for detecting first and higher order diffracted lightof the second wavelength that is diffracted by the optical element,wherein the first diffracted light detection region is arranged suchthat it does not straddle across a region that is divided by a maximumrange or a minimum range of the dilation of zero order light coming fromthe first information recording medium that comes from a recording layerthat differs from the recording layer that is to be recorded orreproduced, and wherein the second diffracted light detection region isarranged such that it does not straddle across a region that is dividedby a maximum range or a minimum range of the dilation of zero orderlight coming from the second information recording medium that comesfrom a recording layer that differs from the recording layer that is tobe recorded or reproduced.

A first optical disk apparatus of the present invention includes anoptical head of the present invention, and a rotating system and amovement system for moving the first and the second informationrecording medium relative to the optical head.

A second optical disk apparatus of the present invention is dedicatedfor reproduction, and includes an optical head of the present invention,a rotating system and a movement system for moving the first and thesecond information recording medium relative to the optical head, andreproducer for reproducing information from signals output from thephotodetector.

A third optical disk apparatus of the present invention is a apparatusfor at least either one of recording and reproducing images from thefirst and the second information recording medium, and includes anoptical head of the present invention, and a rotating system and amovement system for moving the first and the second informationrecording medium relative to the optical head.

A fourth optical apparatus of the present invention is a reproductiondedicated optical disk apparatus for reproducing images from the firstand the second information recording medium, and includes an opticalhead of the present invention, and a rotating system and a movementsystem for moving the first and the second information recording mediumrelative to the optical head.

Furthermore, a computer of the present invention is provided with anoptical disk apparatus of the present invention as an external memoryapparatus.

Furthermore, a server of the present invention is provided with anoptical disk apparatus of the present invention as an external memoryapparatus.

Furthermore, a car navigation system of the present invention isprovided with an optical disk apparatus of the present invention as anexternal memory apparatus.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a diagram for explaining operations when a first light sourceis used in an optical head according to Embodiment 1 of the presentinvention.

FIG. 1B is a diagram for explaining operations when a second lightsource is used in the optical head according to Embodiment 1 of thepresent invention.

FIG. 2A is a diagram showing the state of the light when recording andreproducing dual-layer disks in the optical head according to Embodiment1 of the present invention.

FIG. 2B is a front view of light beams on a light receiving surface ofFIG. 2A.

FIG. 3A is a front view of a photodetector used in the optical head ofEmbodiment 1.

FIG. 3B is a front view of a hologram used in the optical head ofEmbodiment 1.

FIG. 3C is a structural diagram of detection regions and one part of acircuit of the photodetector used in the optical head of Embodiment 1.

FIG. 4A is a diagram for explaining operations when the first lightsource is used in a separate example of the optical head of Embodiment 1of the present invention.

FIG. 4B is a diagram for explaining operations when the second lightsource is used in a separate example of the optical head of Embodiment 1of the present invention.

FIG. 5A is a front view of a photodetector used in a separate example ofthe optical head of Embodiment 1.

FIG. 5B is a front view of a hologram used in a separate example of theoptical head of Embodiment 1.

FIG. 6A is a front view of a photodetector used in a separate example ofthe optical head of Embodiment 1.

FIG. 6B is a front view of a hologram used in a separate example of theoptical head of Embodiment 1.

FIG. 7A is a front view of a photodetector used in a separate example ofthe optical head of Embodiment 1.

FIG. 7B is a front view of a hologram used in a separate example of theoptical head of Embodiment 1.

FIG. 8A is a front view of a photodetector used in an optical head ofEmbodiment 2.

FIG. 8B is a front view of a hologram used in the optical head ofEmbodiment 2.

FIG. 9A is a diagram for explaining the operations of the optical headof Embodiment 3 of the present invention with respect to a firstinformation recording medium.

FIG. 9B is a diagram for explaining the operations of the optical headof Embodiment 3 of the present invention with respect to a secondinformation recording medium.

FIG. 10A is a front view of a photodetector used in the optical head ofEmbodiment 3.

FIG. 10B is a front view of a hologram used in the optical head ofEmbodiment 3.

FIG. 11A is a front view of a photodetector used in an optical head ofEmbodiment 4.

FIG. 11B is a front view of a hologram used in the optical head ofEmbodiment 4.

FIG. 12 is a structural diagram of an optical disk apparatus ofEmbodiment 5.

FIG. 13 is an external view of a computer in which the optical diskapparatus of the present invention is used.

FIG. 14 is an external view of an optical disk recorder in which theoptical disk apparatus of the present invention is used.

FIG. 15 is an external view of an optical disk player in which theoptical disk apparatus of the present invention is used.

FIG. 16 is an external view of a server in which the optical diskapparatus of the present invention is used.

FIG. 17 is an external view of a car navigation system in which theoptical disk apparatus of the present invention is used.

FIG. 18A is a diagram for explaining how to record and reproduce DVDdisks with a conventional optical head.

FIG. 18B is a diagram for explaining one example of how to record andreproduce CD disks with a conventional optical head.

FIG. 19A is a front view of one example of a hologram that is used in aconventional optical head.

FIG. 19B is a front view of one example of a photodetector that is usedin a conventional optical head.

BEST MODE FOR CARRYING OUT THE INVENTION

With the present invention, information reliably can be recorded andreproduced even when recording and reproducing multi-layer disks ofdifferent varieties.

In the optical head of the present invention, it is preferable that atleast one of the first diffracted light detection regions is outside afirst maximum range, which is the maximum range of the dilation of zeroorder light coming from the first information recording medium thatcomes from a recording layer that differs from the recording layer thatis to be recorded or reproduced, and that at least one of the seconddiffracted light detection regions is outside a second maximum range,which is the maximum range of the dilation of zero order light comingfrom the second information recording medium that comes from a recordinglayer that differs from the recording layer that is to be recorded orreproduced. With this configuration, it is possible to avoid the effectof scattered light from other layers of the multi-layer disk, and thusinformation reliably can be recorded and reproduced.

Furthermore, it is preferable that the optical element that diffractslight of the first wavelength and the optical element that diffractslight of the second wavelength are separate elements, that there is ashared region that is shared by both the first diffracted lightdetection region and the second diffracted light detection region, andthat the shared region is arranged outside the larger range of the firstmaximum range and the second maximum range. With this configuration, thepattern of the optical element can be optimized for light of differentwavelengths and it is also possible to share detection regions, and thusthe area of the photodetectors can be decreased and the structure can besimplified.

Furthermore, is it preferable that at least one of the first diffractedlight detection regions and at least one of the second diffracted lightdetection regions are arranged on the inside of the smaller of a firstminimum range, which is the minimum range of the dilation of zero orderlight coming from the first information recording medium that comes froma recording layer that differs from the recording layer that is to berecorded or reproduced, and a second minimum range, which is the minimumrange of the dilation of zero order light coming from the secondinformation recording medium that comes from a recording layer thatdiffers from the recording layer that is to be recorded or reproduced.With this configuration, the offset due to scattered light is about thesame when either recording or reproducing both information recordingmedia, and thus if the amount of the effect due to other layer scatteredlight is calculated in advance and set so as to be eliminated, then theinformation on both information recording media can be recorded andreproduced reliably.

Furthermore, it is preferable that both of all the first diffractedlight detection region and all the second diffracted light detectionregion are arranged inside the smaller range of the first minimum rangeand the second minimum range.

Furthermore, it is preferable that the first diffracted light detectionregion and the second diffracted light detection region are coupledelectrically. With this configuration, it is possible to share an I-Vamp between the first and the second information recording medium, andto simplify the electric circuit.

An embodiment of the present invention is described below with referenceto the drawings. In the diagrams below, the same symbols have beenattached to the same configurations and elements performing the sameoperation.

Embodiment 1

FIG. 1 shows a structural overview of an optical head 20 according tothe present embodiment. FIG. 1A shows a state in which a high densitydisk that has a thin substrate thickness (first information recordingmedium) is recorded and reproduced, and FIG. 1B shows a state in which aDVD disk (second information recording medium) is recorded andreproduced. The optical head 20 is provided with two types of lightsource, a blue semiconductor laser (first wavelength light source) 21whose wavelength is about 400 nm (380 nm-420 nm) and a red semiconductorlaser (second wavelength light source) 22 whose wavelength is 630 nm-680nm.

It should be noted that recording and reproduction means at least one ofeither recording and reproduction, for example the optical head 20 maybe dedicated to reproduction only, or may be used for both recording andreproduction. This fact is also the same in the following descriptions.

In FIG. 1A, a light of λ1 that is emitted from the blue semiconductorlaser 21 passes through a wavelength selection prism 23, and isconverted to parallel light by a collimating lens 24. The light that isconverted to parallel light is reflected by a beam splitter 25, passesthrough a wavelength filter 26 and a ¼ wavelength plate 27, is convertedto convergent light by an objective lens 28, which is a focusing means,and is irradiated onto a high density disk 29.

Here, it has been assumed that the numerical aperture (NA) of theobjective lens 28 is 0.85, and that the substrate thickness of the highdensity disk 29 is 0.1 mm. The objective lens 28 is designed such thataberration is at a minimum when the blue light of wavelength λ1 isirradiated onto a disk having a substrate thickness of 0.1 mm. The lightthat is reflected, diffracted and modulated by the high density disk 29passes again through the objective lens 28, the ¼ wavelength plate 27and the wavelength filter 26, and passes through the beam splitter 25.One part of the light is diffracted by a hologram (optical element) 30,converted to convergent light by a detection lens 31 and is incident ona photodetector 32, which is a light detector. The photodetector 32 hasa plurality of photodetection regions, and outputs a signal inaccordance with the quantity of light that is received.

FIG. 1B is described next. A light of wavelength λ2 that is emitted fromthe red semiconductor laser 22 is reflected by the wavelength selectionprism 23 and is converted to parallel light by the collimating lens 24.The light that is converted to parallel light is reflected by the beamsplitter 25, passes through the wavelength filter 26 and the ¼wavelength plate 27, is converted to convergent light by the objectivelens 28, and is irradiated onto the DVD disk 10.

Here, the numerical aperture (NA) of the light that is irradiated fromthe objective lens 28 is restricted to 0.6 by the wavelength filter 26.The substrate thickness of the DVD disk 10 is 0.6 mm. The light that isreflected, diffracted and modulated by the DVD disk 10 passes againthrough the objective lens 28, the ¼ wavelength plate 27 and thewavelength filter 26, and passes through the beam splitter 25. One partof the light is diffracted by the hologram 30, converted to convergentlight by a detection lens 31 and is incident on the photodetector 32.The photodetector 32 has a plurality of photodetection regions, andoutputs a signal in accordance with the quantity of light that isreceived.

FIG. 2A is a simplified view of the state of the light when recordingand reproducing dual-layer disks. The high density disk 29 is providedwith a first recording layer 33 and a second recording layer 34. FIG. 2Ashows a state in which the light that comes from the objective lens 28is focused on the first recording layer 33. The light that is reflectedfrom the first recording layer 33 passes again through the objectivelens 28, is focused by the detection lens 31 and is focused onto a lightreceiving surface 36, as shown by a light beam 35.

On the other hand, part of the light that passes through the firstrecording layer 33 is reflected by the second recording layer 34, passesthrough the objective lens 28, and is focused by the detection lens 31.This light is scattered light (referred to below as “other layerscattered light”) 37. As shown in FIG. 2A, the other layer scatteredlight 37 is focused in front of the light receiving surface 36, and itis light that spreads over the light receiving surface 36.

FIG. 2B shows a front view of the light beams on the light receivingsurface. The light beam 35 is focused, however the other layer scatteredlight 37 is dilated. The other layer scattered light is dilatedsubstantially circularly, and its radius is R. R can be representedsubstantially as in Expression (1) below in terms of an optical distanced between the first recording layer 33 and the second recording layer34, a focal length Fo and numerical aperture NA of the objective lens28, and the focal length Fd of the detection lens 31. “Substantially”means that R is not limited only to cases in which it is absolutely thesame as the right hand side of the expression below, but also means thatit includes cases in which R is about the same.R=d·NA·Fd/Fo  Expression (1)

Here, Fo=2 mm, Fd=40 mm, NA=0.85, the refractive index of the substancebetween the dual layers of the high density disk is 1.6 and theinterlayer thickness is taken to be 20-30 μm as per the standard. Whenthe interlayer thickness is at its minimum value of 20 μm, d=20/1.6, andthus when the values are substituted into Expression (1), the minimumvalue of the radius R is 213 μm. In the same way, when the interlayerthickness is at the maximum value of 30 μm, d=30/1.6, and the maximumradius R is 319 μm.

Next, in the case of the DVD disk, according to the standard, theinterlayer thickness is 55±15 μm and the refractive index is 1.55±0.10.When the refractive index of the substance between the dual layers is1.65, which is the standard maximum value, and the interlayer thicknessis 40 μm, which is the minimum value according to the standard,d=40/1.65. When the NA of the DVD disk during recording and reproductionis 0.6, and the previous values are substituted into Expression (1), theminimum value of the radius R is 290 μm.

In the same way, when the refractive index of the substance between thedual layers is 1.45, which is the minimum value in the standard, and theinterlayer thickness is 70 μm, which is the maximum value in thestandard, d=70/1.45 and the maximum value of the radius R is 579 μm.

The dual-layer disk is made such that the reflectance of the firstrecording layer 33 and that of the second recording layer 34 aresubstantially the same. That is to say, the film reflectance of thefirst recording layer 33 is substantially the same as the product of thefilm reflectance of the second recording layer 34 times the square ofthe transmittance of the first recording layer 33.

Thus, light that is reflected by the recording layer that is differentfrom the recording layer that is to be recorded or reproduced becomesthe other layer scattered light. The other layer scattered light isweaker than the light that is to be reproduced by the amount that theradius R dilates. However it affects a large area, and if a part of thelight enters the detection area due to diffraction by a hologram, forexample, then a signal corresponding to the other layer scattered light37 is included in the signal that is output from the photodetection areaand this is external noise that cannot be ignored.

In particular, if the other layer scattered light is incident on a partof the detection region, and if the amount of light that is incident onthe detection region changes due to fluctuations in the tilt of thedisk, lens shift or interlayer thickness, then the offset due to thescattered light changes, and may be a factor in causing instability inthe recording and reproduction of information. The radius R is afunction of the optical distance between the layers, as noted above, andthe allowable range of this value is determined by the standard (format)of the optical disk that is to be reproduced. Consequently, if theoptical system is known, then the maximum and minimum values of therange of the dilation radius of the other layer scattered light ascalculated by the above-noted Expression (1) are determined by thetolerance range of the format.

FIG. 3A shows a front view of the photodetector 32. In FIG. 3A, numeral38 denotes the standard maximum range of zero order other layerscattered light created by the hologram 30 when reproducing the highdensity disk 29, which is a dual-layer disk. Numeral 39 denotes thestandard maximum range of zero order other layer scattered light createdby the hologram 30 when reproducing the DVD disk 10, which is adual-layer disk. In the case of the present embodiment, with the valuecalculated by the above-mentioned Expression (1), the maximum range 38is a circular range having a radius of 319 μm. Furthermore, the maximumrange 39 is a circular range having a radius of 579 μm.

A detection region 40 receives zero order light that is not diffractedby the hologram 30. The detection region 40 is used when reproducing thehigh density disk 29 and also when reproducing the DVD disk 10. Adetection region 41 receives that light, of the light that is used whenreproducing the high density disk 29, that is diffracted by the hologram30. The detection region 41 is arranged on an outside region, such thatit does not straddle across the outside region and an inside regiondefined by the standard maximum range 38 of the other layer scatteredlight of the high density disk 29. In the above-noted numerical example,the detection region 41 is arranged outside a range of at most 319 μmfrom the center of the detection region 40.

A detection region 42 receives that light, of the light that is usedwhen reproducing the DVD disk 10, that is diffracted by the hologram 30.The detection region 42 is arranged on an outside region, such that itdoes not straddle across the inside region and an outside region definedby the standard maximum range 39 of the other layer scattered light ofthe DVD disk 10. In the above-noted numerical example, the detectionregion 42 is arranged outside a range of at most 579 μm from the centerof the detection region 40. A RF signal, which is the signal forreproducing information, and four signals used for creating a trackingsignal with the phase difference method are obtained from the detectionregion 40.

A focus signal (spot size detection method (SSD method)) and a trackingsignal (push pull method) that are used when reproducing the highdensity disk 29 are obtained from the detection region 41. A focussignal (SSD method) and a tracking signal (push pull method) that areused when reproducing the DVD disk 10 are obtained from the detectionregion 42.

FIG. 3B schematically shows the hologram 30. The hologram 30 is dividedinto two regions about a central dividing line 43. The push pull methodtracking signal is generated by differentiating between these tworegions. A region on the right side of the dividing line 43 is dividedinto regions 44F and regions 44B, and the hologram 30 generates lightthat is focused in front of the light receiving surface and light thatis focused behind the light receiving surface. A region on the left sideof the dividing line 43 is divided into regions 45F and regions 45B, andthe hologram 30 generates light that is focused in front of the lightreceiving surface and light that is focused behind the light receivingsurface.

The focus signal is generated with the SSD method from the differencebetween the light focused on the front side and the light focused on theback side. The hologram 30 is used both when reproducing the highdensity disk 29 and when reproducing the DVD disk 10. In this case, thediffraction angle differs because the wavelength when reproducing thehigh density disk 29 differs from that when using the DVD disk 10. Thelight is distributed between the detection regions 41 and 42 byutilizing this difference. That is to say, the first order diffractedlight from the blue laser used by the high density disk 29 is receivedby the detection region 41 and the first order diffracted light from thered laser used by the DVD disk 10 is received by the detection region42.

As shown in FIG. 3A, with this configuration, it is possible to reduceexternal interference of the focus signal and the push pull trackingsignal because the detection region 41 can be arranged outside of thestandard maximum range 38 of the other layer scattered light whenreproducing the high density disk 29. In addition, it is possible toreduce external interference of the focus signal and the push pulltracking signal because the detection region 42 can be arranged outsideof the standard maximum range 39 of the other layer scattered light whenreproducing the DVD disk 10.

Since the detection region 41 and the detection region 42 areindependent, it is possible to optimize the detection region 41 for usewith the high density disk 29, and to optimize the detection region 42for use with the DVD disk 10.

FIG. 3C shows the detail of the detection region 41 and the detectionregion 42, and a structural view of part of a circuit. The detectionregion 41 is divided into 12 regions from a region 41 a to a region 41l, and the detection region 42 is divided into 12 regions, from a region42 a to a region 42 l. The region 41 a and the region 42 a are connectedelectrically, and the current signal that is output from the region 41 ais added to the current signal that is output from the region 42 a andinput into an I-V amp (current/voltage converter) 46 and is output as acorresponding voltage signal.

Similarly, the current signal that is output from the region 41 b isadded to the current signal that is output from the region 42 b, inputto an I-V amp 47 and is output as a corresponding voltage signal.Although not illustrated, for the other regions 41 c-41 l, they arerespectively electrically connected to the regions 42 c-42 l, andvoltage signals are output from corresponding I-V amps in accordancewith the amount of light. Further still, since the detection region 41is independent from the detection region 42, the detection region 41 canbe optimized for reproducing the high density disk 29 and the detectionregion 42 can be optimized for reproducing the DVD disk 10.

Since the detection region 41 and the detection region 42 are connectedelectrically, with this configuration it is possible to share the I-Vamp when reproducing the high density disk 29 and when reproducing theDVD disk 10. That is to say, since the signal from the detection region42 is zero when reproducing the high density disk 29, the I-V ampreceives only the signal from the detection region 41. On the otherhand, since the signal from the detection region 41 is zero whenreproducing the DVD disk 10, the I-V amp receives only the signal fromthe detection region 42. With such sharing, it is not necessary toprovide an independent I-V amp for the respective detection region 41and 42, and thus the electrical circuit can be simplified.

Furthermore, since it is possible to reduce the number of signal linesthat are output from the photodetector, the size of the photodetectorpackage can be reduced, it is possible to miniaturize the optical headdevice and the optical information apparatus and to reduce costs.

FIG. 4 shows a structural view of an optical head 50 according to aseparate example. FIG. 4A shows a state of recording and reproducing ahigh density disk, and FIG. 4B shows a state of recording andreproducing a DVD disk. The configuration differs from that of FIG. 1 inthe use of a separate hologram 51 as a substitute for the hologram 30,in that a part of the zero order light of the hologram 51 is diffractedby a further separate hologram 52, and in that these are received by aphotodetector 53.

FIG. 5A shows a front view of the photodetector 53 shown in FIG. 4. Adetection region 54 receives the zero order light that is not diffractedby both of the two holograms 51 and 52. The RF signal, which is thesignal for reproducing the information, is obtained from the light thatis detected by the detection region 54. The light that is not diffractedby the hologram 51 and that is diffracted by the hologram 52 is receivedon a photodetection region 55. Four signals used for creating trackingsignals according to the phase shift method are obtained from the lightreceived by the photodetection region 55. Because detection according tothe phase shift method is not greatly affected by scattered light, thedetection region 55 in the examples in FIGS. 4 and 5 is within the rangeof scattered light.

Detection regions 56 and 57 are arranged on an outside region such thatthey do not straddle across the outside region and an outside regiondefined by the standard maximum range 38 of the other layer scatteredlight of the high density disk 29. The detection regions 56 and 57receive light that is diffracted by the hologram 51 when reproducing thehigh density disk 29. A focus signal (spot size detection method (SSDmethod)) and a tracking signal (push pull method) that are used whenreproducing the high density disk 29 are obtained from the detectionregion 56. Furthermore, a signal for correction offset caused by lensshift of the tracking signal is obtained from the detection region 57.

Detection regions 58 and 59 are arranged on an outside region such thatthey do not straddle across the outside region and an inside regiondefined by the standard maximum range 39 of the other layer scatteredlight of the DVD disk 10. The detection regions 58 and 59 are arrangedeven further out, and receive light that is diffracted by the hologram51 when reproducing the DVD disk 10. A focus signal (spot size detectionmethod (SSD method)) and a tracking signal (push pull method) that areused when reproducing the DVD disk 10 are obtained from the detectionregions 58 and 59.

FIG. 5B shows an overview of the hologram 51. The dotted line in FIG. 5Brepresents the shape of the light beam on the hologram 51. The hologram51 is divided into six regions 60-65. When reproducing high densitydisks, the light of the regions 62 and 63 is diffracted to the detectionregion 56. Although not illustrated, the interior of the regions 62 and63 is divided further into regions for forward focal point use andregions for rear focal point use. When reproducing high density disks,the light of the regions 60, 61, 64 and 65 is diffracted to thedetection region 57. The regions 60, 61, 64 and 65 have substantially nopush pull signal component but include a large change component due tolens shift. Thus, a signal for offset due to lens shift of the trackingsignal can be obtained from the signal obtained from the detectionregion 57.

FIG. 6A shows a front view of a photodetector 70 according to anotherexample. The photodetector 70 shown in FIG. 6A is a photodetector thatis used as a substitute for the photodetector 53 in the configuration inFIG. 4. In addition, the photodetector 70 uses a hologram 72 shown inFIG. 6B as a substitute for the hologram 51. The differences of thephotodetector 70 from the configuration shown in FIG. 5 are describedbelow. A detection region 71 is arranged on an outside region such thatit does not straddle across the outside region and an inside regiondefined by the standard maximum range 38 of the other layer scatteredlight of the high density disk 29. The detection region 71 receives thatlight, of the light that is used when reproducing the high density disk29, that is diffracted by the hologram 72. A focus signal (spot sizedetection method (SSD method)), a tracking signal (push pull method) andalso a spherical aberration detection signal that are used whenreproducing the high density disk 29 are obtained from the detectionregion 71.

A detection region 73 is arranged on an outside region such that it doesnot straddle across the outside region and an inside region defined bythe standard maximum range 39 of the other layer scattered light of theDVD disk 10. The detection region 73 receives that light, of the lightthat is used when reproducing the DVD disk 10, that is diffracted by thehologram. A focus signal (spot size detection method (SSD method)) and atracking signal (push pull method) that are used when reproducing theDVD disk 10 are obtained from the detection region 73.

FIG. 6B shows an overview of the hologram 72. The dotted line in FIG. 6Brepresents the shape of the light beam on the hologram 72. The hologram72 is divided into eight regions 74-81. When reproducing high densitydisks, the light of the regions 76, 77, 78 and 79 is diffracted to thedetection region 71. Although not illustrated, the interior of theregions 76-79 is further divided into regions for front focal point useand regions for rear focal point use. An inner circumferential focussignal is created from the regions 77 and 78 that are close to thecenter of the light beam, and an outer circumferential focus signal iscreated from the regions 76 and 79 that are further from the center. Aspherical aberration detection signal is created from the differentialsignal of both these signals that are created, and a regular focussignal is created from a summation of the signals.

FIG. 7A shows a front view of a photodetector 90 according to stillanother separate example. The photodetector 90 shown in FIG. 7A is aphotodetector that is used as a substitute for the photodetector 53 inthe configuration in FIG. 4. In addition, the photodetector 90 uses ahologram 92 shown in FIG. 7B as a substitute for the hologram 51. Thedifferences of the photodetector 90 from the configurations shown inFIGS. 5 and 6 are described below. A detection region 91 is arranged onan outside region such that it does not straddle across the outsideregion and an inside region defined by the standard maximum range 38 ofthe other layer scattered light of the high density disk 29. Thedetection region 91 receives that light, of the light that is used whenreproducing the high density disk 29, that is diffracted by the hologram92. A focus signal (spot size detection method (SSD method)), a trackingsignal (push pull method) and also a spherical aberration detectionsignal that are used when reproducing the high density disk 29 areobtained from the detection region 91.

A detection region 93 is arranged on an outside region such that it doesnot straddle across the outside region and an inside region defined bythe standard maximum range 39 of the other layer scattered light of theDVD disk 10. The detection region 93 receives that light, of the lightthat is used when reproducing the DVD disk 10, that is diffracted by thehologram 92. A focus signal (semicircle spot size detection method (SSDmethod)) and a tracking signal (push pull method) that are used whenreproducing the DVD disk 10 are obtained from the detection region 93.

FIG. 7B shows an overview of the hologram 92. The dotted line in FIG. 7Brepresents the shape of the light beam on the hologram 92. The hologram92 is divided into twelve regions 94-105. When reproducing high densitydisks, the light of the regions 96-103 is diffracted to the detectionregion 91. The regions 96 and 100 are opposite each other. One of themmakes a beam for a front focal point, and the other makes a beam for arear focal point. This is the same relationship as with regions 97 and101, regions 98 and 102 and regions 99 and 103.

An inner circumferential focus signal is created from the regions 97,98, 101 and 102 that are close to the center of the light beam, and anouter circumferential focus signal is created from the regions 96, 99,100 and 103 that are further from the center. A spherical aberrationdetection signal is created from the differential signal of both thesesignals that are created, and a regular focus signal is created from asummation of the signals.

With the present embodiment, even if optical disks of a different formatinclude a dual-layer disk, it is possible to prevent the other layerscattered light of the dual layers from influencing the focus signal andthe tracking signal, and information can be recorded and reproducedreliably. Moreover, since the photodetector may be made more compact,the cost of the optical head device and the optical informationrecording apparatus can be reduced.

In the present embodiment, since it is possible to utilize a focusingmethod in which the effect on focusing when transversing the tracks issmall, such as the SSD method, it is also possible to record andreproduce information reliably, even in cases when the groove pitch islarger than the spot on the disk, such as with DVD-RAM.

The following is a supplement to the present embodiment, but is the samefor Embodiment 2 and beyond. The focus signal, tracking signal andspherical aberration detection signal are not limited to the exampleshown here. In focusing, alternatively the signals may be combined witha knife edge method or a defocus knife edge method, and in tracking, thesignals may be combined in, for example, a three beam method, ordifferential push pull method (DPP).

Furthermore, specific examples of the focal length of the objective lensand the focal length of the detection lens were given to give numericalvalues to the range of the other layer scattered light, however thepresent invention is not limited to these values. That is to say, therange of the other layer scattered light is determined appropriatelyfrom the optical system and the disk format that actually is used,according to the above-noted Expression (1), and the detection regionscan be arranged in accordance with the range of the other layerscattered light that is calculated.

Furthermore, in the present embodiment, an example has been shown inwhich the detection regions for high density disks and the detectionregions for DVD disks are coupled electrically. However, there is nolimitation to this, and separate I-V amps may be provided to carry outthe current/voltage conversion and the present embodiment may beconfigured with separate outputs. In this configuration, the error ratewhen reproducing information can be reduced since it is possible tooptimize the conversion resistance of the I-V amp separately for thehigh density and for the DVD disks.

Furthermore, in the present embodiment, an example has been given inwhich blue (for example 405 nm) and red (630 to 680 nm) are thewavelengths, however, the effect of the present invention is not limitedto this combination of wavelengths. That is to say, the wavelengthcombination may differ from the example of the present invention, andthe present embodiment may be configured to use disks of a disk formatthat corresponds to the wavelengths.

Furthermore, in the present embodiment, an example has been given ofusing a wavelength filter and a ¼ wavelength plate to make disks havingdifferent substrate thicknesses compatible, however the effect of thepresent invention is not limited to this. The present invention can alsobe applied to methods using dichro-holograms and to cases using phasesteps.

Moreover, the first embodiment has been described using first orderdiffracted light, however the diffracted light may be second or higherorder light. First order light is the lowest order diffracted light, andthe diffraction angle increases with increasing order.

Embodiment 2

Embodiment 2 is an example in which the detection region that receivesthe light used for the focus signal is continually within the range ofthe scattered light. The optical configuration of Embodiment 2 hassubstantially the same configuration as that of FIG. 1, but as thephotodetector, a photodetector 110 shown in FIG. 8A is substituted forthe photodetector 32 of FIG. 1, and a hologram 111 shown in FIG. 8B isused as a substitute for the hologram 30.

FIG. 8A shows a front view of the photodetector 110. A detection region112 receives zero order light that is not diffracted by the hologram111. The detection region 112 is used when reproducing the high densitydisk 29 and when reproducing the DVD 10. That light, of the light usedwhen reproducing the high density disk 29, that is diffracted by thehologram 111 is received by detection regions 113 and 114.

The detection region 113 is arranged on an inside region such that itdoes not straddle across an outside region and the inside region definedby a standard minimum range 115 of the other layer scattered light ofthe high density disk 29. The detection region 114 is arranged on anoutside region such that it does not straddle across the outside regionand an inside region defined by the standard maximum range 38 of theother layer scattered light of the high density disk 29.

Detection regions 116 and 117 receive that light, of the light that isused when reproducing the DVD disk 10, that is diffracted by thehologram 111. The detection region 116 is arranged on the inside regionsuch that it does not straddle across an outside region and the insideregion defined by the standard minimum range 115 of the other layerscattered light of the high density disk 29. The detection region 117 isarranged on an outside region such that it does not straddle across theoutside region and an inside region defined by the standard maximumrange 39 of the other layer scattered light of the DVD disk 10. RFsignal, which is the signal for reproducing the information, and foursignals used for creating tracking signal according to the phasedifferential method are obtained from the detection region 112.

A focus signal (spot size detection method (SSD method)) and a trackingsignal (push pull method) that are used when reproducing the highdensity disk 29 are obtained from the detection region 113. A signal forcorrecting offset due to lens shift of the tracking signal is obtainedfrom the detection region 114. Furthermore, a focus signal (SSD method)and a tracking signal (push pull method) that are used when reproducingthe DVD disk 10 are obtained from the detection regions 116 and 117.

FIG. 8B shows an overview of the hologram 111. The dotted line in FIG.8B represents the shape of the light beam on the hologram 111. Thehologram 111 is divided into six regions 118-123. When reproducing highdensity disks, the light of the regions 120 and 121 is diffracted to thedetection region 113. Although not illustrated, the interior of theregions 120 and 121 further is divided into regions for forward focalpoint use and regions for rear focal point use.

When reproducing high density disks, the lights of the regions 118, 119,122 and 123 are diffracted to the detection region 114. The regions 118,119, 122 and 123 have substantially no push pull signal component butinclude a large change component due to lens shift. Thus, a signal forcorrecting offset due to lens shift of the tracking signal can beobtained from the signal obtained from the detection region 114.

Here, Fo=2 mm, Fd=40 mm, NA=0.85, the refractive index of the substancebetween the dual layers of the high density disk is 1.6 and theinterlayer thickness is taken to be a minimum of 20 μm as per thestandard. In this case, d=20/1.6, and thus when these numerical valuesare substituted into Expression (1), the value of the radius R is 213μm. Next, in the case of the DVD disk, when the refractive index is thestandard maximum value of 1.65, and the interlayer thickness is thestandard minimum of 40 μm, d=40/1.65. When the NA during recording andreproduction of the DVD disk is set to 0.6 and the preceding numericalvalues are substituted into Expression (1), the minimum value of theradius R is 290 μm.

Consequently, the standard minimum range of other layer scattered lightof high density disks is a circle with a radius of 213 μm. Because thisis smaller than 290 μm, which is the minimum standard range of otherlayer scattered light in the case of DVD disks, the minimum range 115 isthe range of the smaller minimum range of either standard.

When the present embodiment is used, the photodetection region forobtaining the signal for focusing is within the range of the other layerscattered light of dual-layer disks, both when reproducing high densitydisks and when reproducing DVD disks. Thus, offset due to scatteredlight exists when reproducing either of the disks, however even if thereis a change between the interlayer thickness of the dual-layer disks,the change in offset is small. That is to say, the offset whenreproducing both disks is about the same, and provided that the amountof the effect caused by the other layer scattered light is calculated inadvance and removed, then even if optical disks of different formatsinclude dual-layer disks it is possible to record and reproduceinformation reliably.

Furthermore, even in this embodiment it is possible to utilize a focusmethod in which the effect on focus when transversing tracks is small,such as the SSD method, and thus it is possible to record and reproduceinformation reliably even in cases, such as with DVD-RAM, in which thegroove pitch is larger than the spot on the disk.

In this configuration, it is possible to join electrically the elementsthat correspond to the detection region 113 for use with the highdensity disk, and the detection region 116 for use with the DVD disk.Thus, the number of amps for changing current signal that come from thedetection regions into voltage signals, and the number of signal linescan be reduced. Thus, it is possible to lower the cost of optical headsand optical disk apparatuses that use this configuration.

Embodiment 3

Embodiment 3 shows an example of sharing a photodetector whenreproducing high density disks and when reproducing DVD disks. FIG. 9shows a structural overview of an optical head 130 of the presentembodiment. The present embodiment differs from Embodiment 1 in that twoindividually separate holograms, a hologram 131 and a hologram 132 areused as a substitute for the hologram 30. The hologram 131 diffractsonly light of the wavelength of the blue semiconductor laser 21, anddoes not diffract light of the wavelength of the red semiconductor laser22. On the other hand, the hologram 132 diffracts only light of thewavelength of the red semiconductor laser 22 and does not diffract thelight of the wavelength of the blue semiconductor laser 21. Light thatis diffracted by the holograms 131 and 132, as well as zero order light,is received by a photodetector 133.

FIG. 10A shows a front view of the photodetector 133. A detection region134 receives zero order light that is not diffracted by the threeholograms 131, 132 and 52. The RF signal, which is a signal forreproducing the information, is obtained from the light that is detectedat the detection region 134. The light that is not diffracted by theholograms 131 and 132, but that is diffracted by the hologram 52 isreceived by a detection region 135. The four signals used for creating atracking signal according to the phase shift method are obtained fromthe light that is received by the detection regions 135. Detectionregions 136 and 137 are arranged on an outside region such that they donot straddle across the outside region and an inside region defined bythe standard maximum range 39 of the other layer scattered light of theDVD disk 10. The detection regions 136 and 137 receive that light, ofthe light that is used when reproducing the high density disk 29, thatis diffracted by the hologram 131.

A focus signal (spot size detection method (SSD method)) and a trackingsignal (push pull method) that are used when reproducing the highdensity disk 29 are obtained from the detection region 136. Furthermore,a signal for correcting offset caused by lens shift of the trackingsignal is obtained from the detection region 137. Furthermore, thedetection regions 136 and 137 also receive light that is used whenreproducing the DVD disk 10 that has been diffracted by the hologram132. A focus signal (spot size detection method (SSD method)) and atracking signal (push pull method) that are used when reproducing theDVD disk 10 also are obtained from the detection regions 136 and 137.

FIG. 10B shows an overview of the hologram 131. The dotted line in FIG.10B represents the shape of the light beam on the hologram 131. Thehologram 131 is divided into six regions 138-143. The light of theregions 140 and 141 is diffracted to the detection region 136. Althoughnot illustrated, the interior of the regions 140 and 141 further isdivided into regions for forward focal point use and regions for rearfocal point use. The light of the regions 138, 139, 142 and 143 arediffracted to the detection region 137. The regions 138, 139, 142 and143 have substantially no push pull signal component but include a largechange component due to lens shift. Thus, a signal for correcting offsetdue to lens shift of the tracking signal can be obtained from the signalobtained from the detection region 137. The hologram 132 is notillustrated, however as a front view, it is divided in substantially thesame way as the hologram 131. However, since the diffracting wavelengthis different, there is a difference in the grating interval of thepattern, for example.

In the present embodiment, it is possible to optimize individually thepattern of the holograms to the high density disk and the DVD diskbecause individual independent holograms are used for the differentwavelengths. Thus, even if optical disks that have different formatsinclude dual-layer disks, then it is possible to record and reproduceinformation reliably.

Furthermore, even in the present embodiment, since it is possible toutilize a focusing method in which the effect on focusing whentransversing the tracks is small, such as the SSD method, it is alsopossible to record and reproduce information reliably even in cases whenthe groove pitch is larger than the spot on the disk, such as withDVD-RAM.

It is also possible to share the detection regions, and thus it ispossible to reduce the area of the photodetector, and at the same timeto decrease the number of amps and the number of pins of the elements.Thus, it is possible to reduce the cost of optical head devices andoptical disk apparatuses by using the optical head according to thepresent invention.

Embodiment 4

In Embodiment 4, an example is described in which a detection regionthat receives the light that is used for the focus signal is usuallywithin range of the scattered light. The optical configuration issubstantially the same as that in FIG. 9, however a photodetector 160shown in FIG. 11A is used as a substitute for the photodetector 133, andholograms 161 and 162 shown in FIG 11B are substitutes for the holograms131 and 132.

FIG. 11A shows a front view of the photodetector 160. Detection regions163 and 164 receive that light, of the light that is used whenreproducing the high density disk 29, that is diffracted by the hologram161. The detection region 163 is arranged on an inside region such thatit does not straddle across an outside region and the inside regiondefined by the standard minimum range 115 of the other layer scatteredlight of the high density disk 29. The detection region 164 is arrangedon an outside region such that it does not straddle across the outsideregion and an inside region defined by the standard maximum range 39 ofthe other layer scattered light of the DVD disk 10.

The detection regions 163 and 164 also receive that light, of the lightthat is used when reproducing the DVD disk 10, that is diffracted by thehologram 162. Four signals used for creating the RF signal, which is thesignal for reproducing the information, and the tracking signalaccording to the phase differential method are obtained from a detectionregion 172. A focus signal (spot size detection method (SSD method)) anda tracking signal (push pull method) that are used when reproducing thehigh density disk 29 are obtained from the detection region 163. Asignal for correcting offset due to lens shift of the tracking signal isobtained from the detection region 164. Furthermore, a focus signal (SSDmethod) and a tracking signal (push pull method) that are used whenreproducing the DVD disk 10 also are obtained from the detection regions163 and 164.

FIG. 11B shows an overview of the holograms 161 and 162. The dotted linein FIG. 11B represents the shape of the light beam on the holograms 161and 162. The hologram 161 is divided into six regions 165-170. The lightof the regions 167 and 168 is diffracted to the detection region 163(during reproduction of high density disks). Although not illustrated,the interior of the regions 167 and 168 is divided further into regionsfor forward focal point use and regions for rear focal point use.

The lights of the regions 165, 166, 169 and 170 are diffracted to thedetection region 164 (during reproduction of high density disks). Theregions 165, 166, 169 and 170 have substantially no push pull signalcomponent but include a large change component due to lens shift. Thus,a signal for correcting offset due to lens shift of the tracking signalcan be obtained from the signal obtained from the detection region 164.

The hologram 162 shows an example of divisions that conform to standardpush pull. The wavelength of light that is diffracted by the hologram162 differs to that of the hologram 161, and thus, for example, thegrating interval of the pattern of the holograms differs.

With the present invention, the photodetection regions for obtaining thesignal for focusing are both within the other layer scattered light ofdual-layer disks, both when reproducing high density disks and whenreproducing DVD disks. Thus, offset due to scattered light exists whenreproducing either of the disks, however even if there is a changebetween the interlayer thickness of the dual-layer disks, the change inoffset is small. That is to say, the offset when reproducing both disksis about the same, and provided that the amount of the effect caused bythe other layer scattered light is calculated in advance and removed,then even when optical disks of different formats include dual-layerdisks, it is possible to reliably record and reproduce information.

Furthermore, even in the present embodiment, since it is possible toutilize a focusing method in which the effect on focusing whentransversing the tracks is small, such as the SSD method, it is alsopossible to record and reproduce information reliably even in cases whenthe groove pitch is larger than the spot on the disk, such as withDVD-RAM.

In the present embodiment, the pattern of the holograms can be optimizedindividually to the high density disk and the DVD disk becauseindividual, independent holograms are used for light of differentwavelengths. Thus, even if optical disks having different formatsinclude dual-layer disks, recording and reproduction of information canbe performed reliably.

Moreover, because the detection regions can be shared, it is possible toreduce the area of the photodetection regions, and at the same time,reduce the number of amps and the number of pin elements. Thus, by usingthe optical head according to the present embodiment, it is possible toreduce the cost of the optical head device and the optical diskapparatus.

It should be noted that in Embodiments 2 and 4, examples were describedin which the detection regions of both the high density disk and the DVDdisk are inside the minimum range of the scattered light, however aconfiguration in which all the detection regions are within the minimumrange of the scattered light is also possible.

Embodiment 5

FIG. 12 shows an overall structural view of an optical disk apparatus(optical disk drive) 150 according to an embodiment of the presentinvention. The optical disk apparatus 150, which is an optical diskapparatus, is provided with an optical head 130. The optical diskapparatus 150 may be dedicated only to reproducing disks, or may becapable of both recording and reproduction.

The optical head 130 may be any one of the above-noted Embodiments 1 to4. The optical disk 29 is fixably clamped by a clamper 151 and aturntable 152, and rotates by a motor (rotating system) 153. The opticalhead 130 rides on a traverse (moving system) 154, and an irradiatedpoint of light is set so as to be movable from an inner periphery to anouter periphery of the optical disk 29.

A control circuit 155 performs focus control, tracking control, traversecontrol and rotation control of the motor, for example, based on thesignal received from the optical head 130. Furthermore, a signalprocessing circuit 156 reproduces information from the reproductionsignal, outputs it to an input/output circuit 157, and transfers thesignal that was received from the input/output signal 157 to the opticalhead 130 via the control circuit 155.

Embodiment 6

FIG. 13 shows a perspective view of a computer according to anembodiment of the present invention. The computer in the diagram isprovided with an optical disk according to Embodiment 5. In FIG. 13, acomputer (personal computer) 1000 includes an optical disk apparatus1001, a keyboard 1003 for inputting information, and a monitor 1002 fordisplaying information.

The computer according to the present embodiment is provided with anoptical disk apparatus according to Embodiment 5 as an external memoryapparatus, and thus it is possible reliably to record and reproduceinformation onto optical disks of different varieties, and may be usedin a wide range of applications.

The optical disk apparatus may be used for backing up a hard disk in thecomputer by making use of its large storage capacity. Furthermore, bymaking use of the low cost and portability of the media (optical disk),and its interchangeability, in which its information can be read out onanother optical disk drive, programs or data can be exchanged with otherpeople, or can be carried for personal use. Furthermore, it can alsohandle reproduction and recording of pre-existing media such as DVDs orCDs.

Embodiment 7

FIG. 14 shows a perspective view of an optical disk recorder (imagerecording apparatus) according to an embodiment of the presentinvention. The optical disk recorder shown in this diagram is providedwith an optical disk apparatus according to Embodiment 5. In FIG. 14, anoptical disk recorder 1010 has an optical disk apparatus according toEmbodiment 5 and is used, connected to a monitor 1011 for displayingrecorded images.

The optical disk recorder according to the present embodiment isprovided with an optical disk apparatus according to Embodiment 5, andthus reliably can record and reproduce images on optical disks ofdifferent varieties, and may be used in a wide range of applications.The optical disk recorder can record images onto media (optical disks),and these may be reproduced at a time of ones choice.

There is no necessity to rewind the optical disk like a tape afterrecording and after reproduction, and chase replay, in which the startof a program can be reproduced while recording that program, andsimultaneous recording / replaying, in which a pre-recorded program isreproduced while recording another program, are possible.

Moreover, by making use of the low cost and portability of the media(optical disk), and its interchangeability, in which its information canbe read out on another optical disk drive, programs or data can beexchanged with other people, or can be carried for personal use.Furthermore, it can also handle reproduction and recording ofpre-existing media such as DVDs or CDs.

It should be noted that the description here is of an optical diskrecorder provided with only an optical disk drive, however an internalhard disk can also be provided, as can a video tape that has a recordingand reproduction function. In this manner, temporary saving or backup ofimages is facilitated.

Embodiment 8

FIG. 15 shows a perspective view of the optical disk player according toan embodiment of the present invention. The optical disk player isprovided with an optical disk apparatus according to Embodiment 5.

In FIG. 15, an optical disk player 1021 is provided with a liquidcrystal monitor 1020, and includes the optical disk apparatus accordingto Embodiment 5. Images that are recorded on optical disks can bedisplayed on the liquid crystal monitor 1020.

The optical disk player according to the present invention is providedwith the optical disk apparatus according to the above-noted Embodiment5, and thus reliably can reproduce optical disks of different varieties,and can be used in a wide range of applications.

Furthermore, the optical disk player can reproduce images, which arerecorded onto media, when desired. There is no necessity to rewind theoptical disk like a tape after reproduction, and images can be accessedand reproduced at a desired location. Furthermore, it can also handlepre-existing media such as DVDs or CDs.

Embodiment 9

FIG. 16 shows a perspective view of a server according to an embodimentof the present invention. The server shown in this diagram is providedwith an optical disk apparatus according to Embodiment 5. In FIG. 16, aserver 1030 includes an optical disk apparatus 1031 according toEmbodiment 5, a monitor 1033 for displaying information and a keyboard1034 for inputting information. The server is connected to a network1035.

The server according to the present embodiment is provided with theoptical disk apparatus according to Embodiment 5 as an external memoryapparatus, and thus it reliably can record and reproduce informationfrom disks of different varieties, and can be used in a wide variety ofapplications.

Making use of the large capacity of optical disks, information (such asimages, speech, moving images, HTML text and text documents) that isrecorded on the optical disk is transmitted in response to a demand fromthe network 1035. Furthermore, information that is sent from the networkis recorded in the requested position. Furthermore, since it is alsopossible to reproduce information that is recorded on pre-existingmedia, such as CDs and DVDs, it is also possible to transmit thatinformation.

Embodiment 10

FIG. 17 shows a perspective view of a car navigation system according toan embodiment of the present invention. The server shown in this diagramincludes an optical disk apparatus according to Embodiment 5. In FIG.17, a car navigation system 1040 includes the optical disk apparatusaccording to Embodiment 5, and is used, connected to a liquid crystalmonitor 1041 for displaying topographical and destination information.

The car navigation system according to the present embodiment isprovided with the optical disk system according to Embodiment 5, andthus images reliably can be recorded and reproduced from different typesof optical disks, and it can be used over a wide range of applications.The car navigation system 1040 calculates its present position based oninformation from map information recorded on a medium(optical disk), ageo-positioning system (GPS) or a gyroscope, a speedometer and anodometer, and displays that position on the liquid crystal monitor.Furthermore, if the destination is input, the system calculates theoptimum route to the destination based on the map information and theroad information, and displays this on the liquid crystal monitor.

By using a large capacity optical disk to record the map information, itis possible to provide detailed road information covering a wide area ona single disk. Furthermore, information about restaurants, conveniencestores and petrol stations that are in the vicinity of the roads canalso be simultaneously provided, contained on the optical disk.

Moreover, with the passage of time, road information becomes old andinaccurate, however since optical disks are interchangeable, and themedia is cheap, the latest information can be obtained by substitutionwith a disk containing the newest road information. Furthermore, sincethe car navigation system can handle the recording and reproduction ofpre-existing media such as DVDs and CDs, it is possible to watch moviesor listen to music inside the vehicle.

INDUSTRIAL APPLICABILITY

With the present invention as noted above, even if optical disks ofdifferent formats include dual-layer disks, the effect of scatteredlight can be suppressed to a small amount, information can be recordedand reproduced reliably, and thus the present invention is useful, forexample, in optical disk apparatus, optical disk recorders, optical diskplayers, server and car navigation systems.

1. An optical head comprising: a first light source that emits light ofa first wavelength for at least either one of recording and reproducinginformation of a first information recording medium; a second lightsource that emits light of a second wavelength for at least either oneof recording and reproducing information of a second informationrecording medium; an optical element for diffracting light of the firstand the second wavelength; and a photodetector that is provided with adetection region for detecting light that is reflected by the firstinformation recording medium or the second information recording medium,and that passes through the optical element; wherein the firstinformation recording medium and the second information recording mediumare multi-layer disks having at least two recording layers; wherein thedetection region includes a first diffracted light detection region fordetecting one of first and higher order diffracted light of the firstwavelength that is diffracted by the optical element, and a seconddiffracted light detection region for detecting one of first and higherorder diffracted light of the second wavelength that is diffracted bythe optical element; wherein the first diffracted light detection regionis arranged such that it does not overlap an outline of a spot on thephotodetector of zero order light coming from the first informationrecording medium that comes from a recording layer that differs from therecording layer that is to be recorded or reproduced; wherein the seconddiffracted light detection region is arranged such that it does notoverlap an outline of a spot on the photodetector of zero order lightcoming from the second information recording medium that comes from arecording layer that differs from the recording layer that is to berecorded or reproduced; wherein the spot on the photodetector changesfrom a minimum range to a maximum range; wherein each of the firstdiffracted light detection region and the second diffracted lightdetection region includes a plurality of diffracted light detectionregions; wherein both of all the first diffracted light detectionregions and all the second diffracted light detection regions arearranged inside the smaller range of a first minimum range, which is theminimum range of the spot on the photodetector of zero order lightcoming from the first information recording medium that comes from arecording layer that differs from the recording layer that is to berecorded or reproduced, and a second minimum range, which is the minimumrange of the spot on the photodetector of zero order light coming fromthe second information recording medium that comes from a recordinglayer that differs from the recording layer that is to be recorded orreproduced.
 2. An optical disk apparatus comprising: an optical headaccording to claim 1, and a rotating system and a movement system formoving the first and die second information recording medium relative tothe optical head.